Transmission

ABSTRACT

The invention relates to a transmission for adjusting a first rotary member relative to a second rotary member with a drive shaft that is concentric with the first and the second rotary member.  
     A high gear reduction ratio combined with small dimensions and a robust design may be achieved in such a way that the drive shaft is connected to a spindle on which a pull member is wound, and that one end of said pull member is firmly connected to said first rotary member and that the pull member is diverted over at least one deflection pulley which is firmly connected to said second rotary member.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a transmission for adjusting a first rotary member relative to a second rotary member with a drive shaft that is concentric with the first and the second rotary member.

[0002] In motive power engineering it is in many cases necessary to move two parts which are pivotal relative to each other against a relatively great moment. In certain cases it is hereby necessary to have the driving torque made available at a shaft which is coaxial to the swivelling axis of the two parts. A well-known transmission of this type is the so-called Harmonic Drive. In such a transmission, a flexible elliptical gear meshes with a rigid circular ring gear. A change in the shape of the gear is effected by a special rolling bearing with an elliptical inner ring. A very high gear reduction ratio is obtained by the fact that the gear has only insignificantly fewer teeth than the ring gear. In this way it is possible to transmit relatively great moments with a single-stage transmission of compact design. U.S. Pat. No. 4,106,371 A and EP 0 773 106 A describe function and application cases of such transmissions.

[0003] When subjected to impulsive loads, the relatively fine teeth of Harmonic Drives may be damaged and/or the engaged teeth may slip, which results in a malfunction of said transmission.

DESCRIPTION OF PRIOR ART

[0004] GB 2 243 203 A, WO 92/04532 and WO 92/00441 disclose devices for adjusting the phase angle of a camshaft which have a flexible member or a lever arrangement inserted between a drive gear and the camshaft. The phase angle of the camshaft may be adjusted by way of a braking device. Such devices increase fuel consumption since energy is dissipated in the braking device. Moreover, the driving torque of camshafts may momentarily become negative which may result in unintended gear shifting on the prior art devices.

[0005] GB 497 749 A describes a transmission for driving variable disk capacitors for which a high speed ratio is achieved by way of a cable pull. A relative adjustment of two movable parts is not provided though.

[0006] In addition, EP 0 041 708 A, EP 0 016 331 A and U.S. Pat. No. 5,040,651 A as well as U.S. Pat. No. 2,005,655 describe flexible coupling elements in which the resilience of one or several cable pulls is used to compensate for jerks. A device for adjusting the phase angle of a camshaft cannot be realized in this way, though.

[0007] U.S. Pat. No. 3,691,871 describes a transmission that employs a pull band which is wrapped around various shafts. Since the transmission of force is essentially based on friction, high torques cannot be transmitted without incurring the risk of changing the phase angle, which makes it unsuitable for adjusting the phase angle of a camshaft. The case is quite similar with the solution disclosed in WO 98/32993 A.

[0008] Additional solutions utilizing pull chains wound around various sprocket wheels have been described in U.S. Pat. No. 3,307,415 A, DE 34 15 584 and WO 95/21340. The common feature of these solutions is that, when the chain is subjected to a greater load, an extension of said chain is to be expected, which results in an inadmissible play. Furthermore, such solutions are complicated and require space which, in many cases, is not available.

[0009] Moreover, U.S. Pat. No. 4,540,223 A discloses a mechanism for connecting two relatively rotatable parts. With such a device, a transmission of torques is not possible in a technically meaningful manner.

SUMMARY OF THE INVENTION

[0010] It is the object of the present invention to avoid these disadvantages and to provide a transmission which is robust, has no or only little clearance and which may be developed with very high gear reduction ratios.

[0011] According to the invention, it is provided that a drive shaft is connected to a spindle on which a pull member is wound, and that one end of the pull member is firmly connected to the first rotary member and that the pull member is diverted over at least one deflection pulley which is firmly connected to the second rotary member. Since the transmission of the invention has no cogwheels, no face play can occur. By selecting the appropriate material for the pull means, it may be obtained from said pull means that, thanks to its own elasticity, it compensates for and attenuates jerky strains so that long service life is achieved even under rough operating conditions.

[0012] An even transmission of torque in either direction may be obtained by winding two pull members on the spindle in opposite directions, the ends of said pull members being each firmly connected to the first rotary member and the pull members being diverted over a deflection pulley firmly connected to the second rotary member.

[0013] In a particularly preferred embodiment of the invention there is provided a pull member having the shape of a band. This permits to transmit high torques under light load conditions in the region of the deflection pulleys.

[0014] Alternatively, it may also be provided that the pull member is designed as a cable. The advantage of using a cable is that it may be helically wound on the spindle without the winding diameter being changed.

[0015] In order to achieve a particularly high gear reduction ratio, it is provided that the distance of the fastening point of the pull member on the first rotary member as well as the distance of the axis of the deflection pulley from the common axis relative to the diameter of the spindle are great. It is thereby particularly advantageous when the distance of the fastening point of the pull member from the common axis is equal to five to fifty times, preferably ten to thirty times, the diameter of the spindle.

[0016] When using a band-shaped pull means, it has to be taken into consideration that the winding diameter slightly changes subject to the length of the wound up tape. If no further measures are taken, this causes the speed ratio to change via the adjusting range of the transmission. Additionally, the speed ratio depends on the respective relative angular position of the rotary members. Should such an effect be unwanted, a drop cam for guiding the pull member may be provided on the first rotary member in the region of the fastening point of the pull member. By designing the drop cam accordingly, it may be obtained that the speed ratio be roughly constant over the entire adjusting range. In specific applications, the design of the drop cam may effect a purposeful change in the speed ratio by way of the adjusting range.

[0017] A particularly high speed ratio may be achieved by guiding the pull member over several deflection pulleys which are alternately linked to the first rotary member and to the second rotary member. The pull member is hereby guided to and fro between the deflection pulleys in the manner of a pulley block.

[0018] In case the resiliency of the pull member is not sufficient to make certain of a play-free operation of the transmission, a tension member may be provided for biasing the pull member.

[0019] The present invention also relates to a device for adjusting the phase angle of a camshaft of an internal combustion engine in which the camshaft is adjustable relative to a drive gear. According to the invention, there is provided the use of a transmission of the type described above, the camshaft being firmly connected to the first rotary member and the drive gear being firmly connected to the second rotary member.

[0020] The transmission described herein above is particularly suitable for use in devices for adjusting the phase angle of camshafts. Its compact and at the same time robust design combined with a high speed ratio and play-free operation make it perfectly suited for use in internal combustion engines.

[0021] It is hereby particularly propitious when an electric motor for adjusting the phase angle of the camshaft is connected to the drive shaft of the transmission. It is advantageous when, in this connection, a housing of the electric motor is firmly connected to the camshaft or to the drive gear. The electric motor which rotates in synchronism is driven by induction through slip rings for example or without contact.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The invention will now be described further, by means of embodiments illustrating examples thereof and represented in the Figures, in which:

[0023]FIG. 1 shows a sectional view of a transmission according to the invention in schematic form;

[0024]FIG. 2 shows an axonometric exploded view of another embodiment of the invention;

[0025]FIG. 3 shows and axonometric view of the transmission of FIG. 2;

[0026]FIG. 4 shows a side view of the transmission of FIG. 2 and 3;

[0027]FIG. 5 shows a view similar to FIG. 1 of another embodiment of the invention and

[0028]FIG. 6 shows a device for adjusting the phase angle of the camshaft of an internal combustion engine according to the invention in schematic form.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] In the embodiment of FIG. 1, a first rotary member 1 is carried in bearings relative to a second rotary member 2 shown in a dashed outline so as to be pivotal about an axis 3. A spindle 4 is provided which is concentric with the axis 3 and on which a pull member 5, consisting of a steel strip or of a steel cable, is arranged in such a manner that it may be wound thereon. At 6 the pull member 5 is firmly attached to the spindle 4. Starting from the spindle 4, the pull member 5 extends past a deflection pulley 7 which is arranged on the second rotary member 2 so as to be pivotal about an axis 7 a to a drop cam 8 which is firmly connected to the first rotary member 1. The pull member 5 is firmly connected to the drop cam 8 at 8 a.

[0030] With the help of FIG. 1, the function of the transmission according to the invention may be explained as follows:

[0031] The pull member 5 is wrapped about the spindle 4 by rotating the spindle 4 clockwise. The thus generated tensile stress causes the pull members 1 and 2 to rotate in opposite directions in such a manner that the distance between the deflection pulley 7 and the drop cam 8 becomes shorter. In case for example, the first rotary member 1 is stationary, the second rotary member 2 is thus rotated counterclockwise. The speed ratio substantially equals the double ratio of the standard distance r of the pull member 5 in the area between the deflection pulley 7 and the drop cam 8 from the axis 3 to the diameter D of the spindle 4. If the pull member 5 is a steel strip, the diameter D of the spindle 4 in this calculation has to be adjusted by the respective thickness of the winding.

[0032] It has to be noticed that the transmission of FIG. 1 allows a torque to be transmitted in only one direction. In order to achieve a two-sided torque transmission, it is necessary to arrange another pull member (not shown) mirror-inverted.

[0033] In the embodiment of FIGS. 2, 3 and 4 there are provided two spindles 4 a and 4 b that mesh with cogwheels 9 a and 9 b on a pinion 10 which is rigidly connected to the drive shaft 11. An additional gear reduction ratio is thus generated which is added in a multiplicative manner to the reduction ratio of the proper transmission. The spindles 4 a, 4 b are symmetrically carried in bearings in the second rotary member 2, which carries four deflection pulleys 7. One pair of pull members 5 aa, 5 ab; 5 ba, 5 bb are wound in opposite directions about each of the spindles 4 a, 4 b and are guided around one deflection pulley 7 each. Pins 12 are shaped on a first rotary member 1, the pull members 5 aa, 5 ab; 5 ba, 5 bb being connected to said pins.

[0034] By rotating the drive shaft 11 in one direction, the pull members 5 aa and 5 ba for example wind off the spindles 4 a and 4 b while at the same time the pull members 5 ab and 5 bb wind on said spindles, a torque being thus generated between the rotary members 1, 2. By reversing the direction of rotation of the drive shaft 11, a torque is created about the opposite direction.

[0035] A face clearance generally occurs between the pinion 10 and the cogwheels 9 a, 9 b, but it is reduced by the secondary transmission by a factor corresponding to the gear reduction ratio. As a result, no adverse effects are commonly to be expected.

[0036] In the embodiment of FIG. 5, a pull means 5 is consecutively guided, starting from the spindle 4, about three deflection pulleys 7 a, 7 b and 7 c and is finally attached to a pin 12 which is rigidly connected to the first rotary member 1. The first and the third deflection pulleys 7 a and 7 c are hereby arranged on the second rotary member 2, whereas the second deflection pulley 7 b is rigidly connected to the first rotary member 1. The arrangement of FIG. 5 permits to obtain a multiple transmission in the way of a pulley block so that an overall considerably increased reduction ratio is achieved. By arranging a second pull member 5 in an opposite direction, a torque may be transmitted in either direction.

[0037]FIG. 6 shows a device for adjusting the phase angle of a camshaft of an internal combustion engine in schematic form. The camshaft is indicated at 20 and is connected to a first rotary member 1 of the transmission described herein above. The second rotary member 2 of the transmission is connected to a drive gear 21 on which a cog belt or a chain that are not illustrated in the drawings herein are running. The drive shaft 11 is driven by an electric motor 22 which is non-rotatably connected to the drive gear 21 and which is supplied with current through slip rings 23.

[0038] When the electric motor 22 is not driven, the camshaft 20 is driven in synchronism with the drive gear 21. The rotation of the drive shaft brought about by the electric motor 22 may cause the camshaft 20 to be adjusted in advance or subsequently which varies the timing of the valves of the combustion engine (not shown) controlled by the camshaft 20. Thanks to the high gear reduction ratio of the transmission in accordance with the invention, a relatively small electric motor 22 is sufficient to produce the appropriate adjusting moments.

[0039] The transmission according to the invention permits in particular to adjust the phase angle of the camshaft of a combustion engine in a play-free, efficient and fast manner. The transmission thereby is robust and of small size. The adjustment of the valve timing permits to reduce fuel consumption and exhaust emission of combustion engines. 

What is claimed is:
 1. A transmission for adjusting a first rotary member relative to a second rotary member with a drive shaft that is concentric with the first and the second rotary member, wherein a drive shaft is connected to a spindle on which a pull member is wound, and wherein one end of said pull member is firmly connected to said first rotary member and wherein the pull member is diverted over at least one deflection pulley which is firmly connected to said second rotary member.
 2. A transmission according to claim 1 , wherein two pull members are wound on the spindle in opposite directions, the ends of said pull members being each firmly connected to said first rotary member and the pull members being each diverted over a deflection pulley firmly connected to said second rotary member.
 3. A transmission according to claim 1 , wherein said pull member has the shape of a band.
 4. A transmission according to claim 1 , wherein said pull member is designed as a cable.
 5. A transmission according to claim 1 , wherein the distance of the fastening point of the pull member on said first rotary member as well as the distance of the axis of the deflection pulley from the common axis relative to the diameter of the spindle are great.
 6. A transmission according to claim 5 , wherein the distance of the fastening point of the pull member from the common axis is equal to five to fifty times, preferably ten to thirty times, the diameter of the spindle.
 7. A transmission according to claim 1 , wherein a drop cam for guiding the pull member is provided in the region of the fastening point of the pull member.
 8. A transmission according to claim 1 , wherein the pull member is guided over several deflection pulleys which are alternately linked to the first rotary member and to the second rotary member.
 9. A transmission according to claim 1 , wherein a tension member is provided for biasing the pull member.
 10. A device for adjusting the phase angle of a camshaft of an internal combustion engine in which the camshaft is adjustable relative to a drive gear, wherein a transmission according to one of the claims 1 through 9 is provided, the camshaft being firmly connected to the first rotary member and the drive gear being firmly connected to the second rotary member.
 11. A device according to claim 10 , wherein an electric motor for adjusting the phase angle of the camshaft is connected to the drive shaft of the transmission.
 12. A device according to claim 11 , wherein a housing of the electric motor is firmly connected to the camshaft or to the drive gear. 